[EM] IRV vs Condorcet vs Range/Score

[Aaron Armitage]

--- On Sun, 10/12/08, Chris Benham <cbenhamau at yahoo.com.au> wrote:

> From: Chris Benham <cbenhamau at yahoo.com.au>
> Subject: [EM] IRV vs Condorcet vs Range/Score
> To: "EM" <election-methods at lists.electorama.com>
> Date: Sunday, October 12, 2008, 11:18 PM
> >"Low social utility (SU)" Condorcet winners
> with
> >little solid support and depend for their status as the
> CW on weakly-held 
> >lower preferences can begin to look quite chimera-like
> and not necessarily the
> >only legitimate winner.
> >
> 
> This seems to be a typical complaint that Condorcet will
> elect a
> compromise rather than a candidate that anyone is excited
> about. But if a
> candidate people are excited about assumes office over the
> CW, then by
> definition the majority is ruled against its will by an
> enthusiastic
> minority. Even supposing that this majority is itself
> composed of
> incompatible minorities does not mean that a polity whose
> electorate is
> broken into several minority factions should just let one
> of those
> factions govern. Wouldn't the acceptable compromise be
> fairer and more
> stable?
> 
> CB: Not necessarily, no. I have in mind something like
> (with sincere ratings):
> 
> 49: A(99)  > C(2)  > B(1)
> 48: B(99)  > C(2)  > A(1)
> 03: C(99) > A(98) > B(1)
> 
> C is the CW, but A is a much more stable, much higher SU,
> arguably as
> fair or fairer winner.
> 

Any strategically informed voter will give approval-like ratings, and will
approve the top two frontrunner he likes better, as well as any candidates
he prefers to that frontrunner, which means that the stated ratings will
look like that regardless of the real ones and a range election will tend
to produce that result regardless of how much utility voters attach to
each candidate. And, of course, IRV produces the same result.

What you're suggesting, then, is a case where the sincere ratings just
happen to match the stated ratings that would be produced by strategic
voting, and that in this special case the strategic voting under range or
approval will look legitimate in elected A over C despite the existence of
a majority coalition for C over A. But range and approal must assume that
this is always the case, when it almost never is.

> Perhaps you (Aaron) could answer my direct question about
> what you
> mean by  "Smith/IRV".
> 

I don't appreciate the tone of this demand.

Nevertheless, I mean we would first check to see who is in the Smith set.
If there's only one, he is the Condorcet winner and is elected. If not, we
eliminate all non-Smith candidates and the lowest Smith set member. Then
repeat until a winner emerges.